Add-on sync allows you to easily keep the same set of Firefox add-ons on all of your devices. When enabled, add-on sync will install, uninstall, enable or disable add-ons on all Sync-connected devices as you make changes to them. For example, if you install Adblock Plus on one computer, Adblock Plus will get installed on your other computers.

Add-on sync only works between similar Firefox installations. For example, if you install an add-on on desktop Firefox, it will only sync to other desktops, not to your Android device running Firefox.

Turning on add-on sync

If you haven't set up a Sync account yet, add-on sync will be turned on when you create your account (see How do I set up Sync on my computer?). If you already have a Sync account, you can enable (or check the status of) add-on sync by following these simple steps on all the devices that have add-ons that you want to sync.

Note: Add-on sync currently only works on desktop Firefox and Firefox for tablets. It doesn't work on Firefox for smaller mobile devices.

These instructions are for desktop Firefox.

At the top of the Firefox window, click on the Firefox button and then select Options.At the top of the Firefox window, click on the Tools menu and then select Options.On the menu bar, click on the Firefox menu and select Preferences....At the top of the Firefox window, click on the Edit menu and select Preferences.

Click the menu button
and choose Options.Preferences.

Select the Sync panel.

In the Sync section, check the check box next to Add-ons.

Click OK to close the Options window.Click Close to close the Preferences window.Close the Preferences window.Close the about:preferences page. Any changes you've made will automatically be saved.

Which add-ons will be synced?

If you install add-ons directly from https://addons.mozilla.org, your add-ons should always sync.
Add-ons installed from other sites or installed by other programs (your security software, for example) will not be synchronized.